In the case of biological and pharmaceutical materials, it is frequently necessary to store the materials completely dry until they are used. These sensitive substances are mostly only obtainable by freeze drying. Furthermore, as a rule, it is necessary to keep these substances completely free from micro-organisms not only because of the decomposition of biological substances brought about by micro-organisms but also in order to prevent possible infections in the case of their use.
The freeze drying of biological and pharmaceutical materials is generally known (see also Ullmanns Enzyklopadie der Technischen Chemie, 3rd edition, Vol. I, p. 556 et seq.). In order to avoid a contamination of the dried material with micro-organisms and other contaminants, laborious apparatus and process-technical measures have to be made.
In the case of drying pharmaceutical preparations in ampoules or small bottles, the procedure is, for example, to provide small bottles which contain the frozen material with a bacterial filter and to dry the material in the small bottles in a first drying step to such an extent that the sublimation of the frozen solvent is concluded.
Subsequently, in a second drying stage, i.e. the so-called post or residual drying, the still remaining residual moisture is removed from the material. Since this second drying step is usually carried out in a special apparatus, the ampoules or vials must be removed from the first drying apparatus in a further working step which is prone to contamination and introduced into the second drying apparatus. For this purpose, the bacterial filter is removed and replaced by an aluminium cap provided with a rubber diaphragm and a hollow needle. After a residual drying for several days depending upon the nature of the material to be dried, the drying chamber is filled with an inert gas and with slight overpressure and the diaphragm opening closed as vapour-tightly as possible by a grouting mass.
Since the speed of sublimation in the case of this type of freeze drying is only about half as great as that of openly spread out material, the freeze drying of biological and pharmaceutical material is also carried out on plates under sterile conditions. A solution of the material to be dried is thereby first sterilised, for example by filtration over a sterile filter, subsequently poured under sterile conditions on to plates and freeze dried by means of known methods. However, a prerequisite of this process is that the whole of the freeze drying plant can be sterilised. Furthermore, it is also necessary to keep the surroundings of the drying plant free from micro-organisms.
After drying has taken place, it is necessary to remove the material in the drying plant itself or in its surroundings with mechanical processes from the plates under sterile conditions and to fill it into also sterile storage containers. This process requires laborious plant and sterile chambers, as well as an especially careful working with the material to be dried or already dried until it is confectioned ready for use.